INTENSIVE TRAINING AND CARDIAC AUTONOMIC CONTROL IN HIGH-LEVEL ATHLETES

Purpose: We aimed to evaluate in a longitudinal study the effect of in tensive training on cardiac autonomic control in athletes using 24-h h eart rate variability analysis. Methods: Time and frequency domain mea sures of heart rate variability were calculated from 24-h Holter monit oring in 15 high level bicyclists (mean age 21 +/- 4 yr) after 1 month of detraining and after 5 months of vigorous training. At the same ti mes echocardiographic left ventricular mass and dimensions and maximal oxygen consumption (VO2max) were assessed. Results: In detrained athl etes, VO2max values, left ventricular mass and dimensions, and time an d frequency domain measures of vagal modulation of heart rate were hig her than in a group of untrained subjects of similar age while heart r ate and the low-to-high frequency ratio were lower, indicating an enha nced vagal modulation of heart rate in athletes as compared with that in control subjects. After 5 months of vigorous training, left ventric ular mass and dimensions and VO2max increased in athletes, while heart rate decreased further. In contrast, no changes were detectable in ti me and frequency domain measures of heart rate variability over the en tire 24-h and in both waking and sleeping hours. Conclusions: This stu dy demonstrates that an increased cardiac vagal control is detectable in detrained athletes; however, after intensive training, despite a si gnificant decrease in heart rate, time and frequency domain measures o f heart rate variability reflecting cardiac vagal control remain uncha nged. Thus, other mechanisms than changes in cardiac autonomic control could be involved in determining the profound bradycardia of athletes .